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 Table of Contents  
ORIGINAL ARTICLE
Year : 2014  |  Volume : 26  |  Issue : 3  |  Page : 253-259

Comparative study of cone-beam computed tomography and multislice computed tomography in the radiographic evaluation of cysts and tumors of the jaws


1 Department of Oral Medicine and Radiology, Chatrapati Shahu Maharaj Shikshan Sanstha's (CSMSS) Dental College and Hospital, Aurangabad, India
2 Department of Oral Medicine and Radiology, Sharad Pawar Dental College and Hospital, Wardha, India
3 Department of Interventional Radiology, Jawaharlal Nehru Medical College and Hospital, Wardha, India
4 Department of Oral Medicine and Radiology, VSPM Dental College and Hospital, Nagpur, Maharashtra, India
5 Department of Periodontics, Bhabha Dental College and Hospital, Bhopal, Madhya Pradesh, India

Date of Submission01-Apr-2014
Date of Acceptance09-Nov-2014
Date of Web Publication19-Nov-2014

Correspondence Address:
Sunil S Mishra
Department of Oral Medicine and Radiology, Chatrapati Shahu Maharaj Shikshan Sanstha's (CSMSS) Dental College and Hospital, Kanchanwadi, Paithan Road, Aurangabad - 431 001, Maharashtra
India
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Source of Support: DMIMSU, Nagpur., Conflict of Interest: None


DOI: 10.4103/0972-1363.144995

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   Abstract 

Aim and Objectives: To assess the efficacy of cone-beam computed tomography (CBCT) in comparison with multislice-computed tomography (MSCT) in the radiographic evaluation of cysts and tumors of the jaws. Materials and Methods: The study was conducted on 25 subjects diagnosed histopathologically with cysts or tumors of the jaws. They were subjected to MSCT and CBCT. The image pairs obtained were compared for diagnostic quality and dimensional accuracy. Also radiation monitoring was done with a newly devised calculative method. Statistics: Descriptive statistical analysis was carried out for all the groups in this study. The Kappa coefficient (k) for intraclass agreement was used for evaluating the scorings given by the evaluator for the diagnostic quality of the image. Results: A total of 28 lesions were found in 25 subjects. The diagnostic quality assessment suggested that the appearance of the internal structure and the soft tissue resolution of CBCT were inferior to MSCT. The radiation dosages from CBCT were noticeably less than MSCT. The dimensional accuracy of CBCT images was found to match those of the MSCT images. Conclusion: The results from the present study showed that CBCT could provide an image with MSCT-comparable diagnostic quality and accuracy, with a lesser radiation dose and risk, at a lower cost.

Keywords: Cone-beam computed tomography, monitoring, multislice-computed tomography, radiation


How to cite this article:
Mishra SS, Degwekar SS, Banode PJ, Bhowate RR, Motwani MB, Mishra PS. Comparative study of cone-beam computed tomography and multislice computed tomography in the radiographic evaluation of cysts and tumors of the jaws . J Indian Acad Oral Med Radiol 2014;26:253-9

How to cite this URL:
Mishra SS, Degwekar SS, Banode PJ, Bhowate RR, Motwani MB, Mishra PS. Comparative study of cone-beam computed tomography and multislice computed tomography in the radiographic evaluation of cysts and tumors of the jaws . J Indian Acad Oral Med Radiol [serial online] 2014 [cited 2021 Dec 7];26:253-9. Available from: https://www.jiaomr.in/text.asp?2014/26/3/253/144995


   Introduction Top


In the last three decades, ever since the breakthrough in 1982, at the Mayo Clinic Biodynamics Research Laboratory, several cone-beam computed tomography (CBCT) systems have been developed. [1] The recent CBCT systems with reduced radiation exposure, provide high-contrast images, which are almost equal to bone window computed tomography (CT). This has resulted in an increase in the indications for CBCT application in the evaluation of the orofacial structures. [2] However, the use of CBCT as a diagnostic imaging modality for benign and malignant tumors is not reported well in literature and only a few studies and case reports of the bony lesions of the cysts and tumors in the jaws, imaged using CBCT, have been documented. [3],[4],[5],[6],[7],[8],[9],[10],[11],[12],[13]

However, a presumably lower radiation dose, lower cost, and CT-equivalent image quality, justifies the surge of interest in the use of CBCT as a substitute for CT scans, for high-contrast structures and lesions. [14],[15],[16] This study intends to verify whether CBCT has an advantage of a lower radiation dose in terms of the absorbed dose and effective dose, lower cost as compared to multislice computed tomography (MSCT), with a substantial diagnostic image quality encompassing the internal structure of the lesions, margins of the lesions, subjective image quality, and findings of artifacts, as well as MSCT. This study also intends to evaluate and compare its accuracy and reproducibility in linear measurements with a MSCT scanner.


   Materials and Methods Top


This study was designed as a cross-sectional, hospital-based study, with a sample size of 25 patients, and carried out in the Department of Oral Medicine and Radiology, Sharad Pawar Dental College and Hospital, TIFAC Core Catheter Laboratory and Department of Radiodiagnosis, AVB Rural Hospital, Sawangi (Meghe), Wardha, Maharashtra. The protocol of the study was approved by the Institutional Ethical Committee of the Datta Meghe Institute of Medical Sciences, Nagpur.

The subjects were selected based on the following criteria:

Inclusion criteria

  • Patients whose panoramic radiograph showed lytic lesions suspected as cysts or tumors involving the jaws
  • Patients who were histopathologically diagnosed with cysts or tumors (benign/malignant) involving the jaws


Exclusion criteria

  • Pregnant females and patients with maxillofacial trauma were excluded


The equipment used for CT scanning was Philips Brilliance 16 Slice Cardiac MDCT, [17] and for the CBCT procedure, Philips Allura Xper FD20 was used. The three-dimensional (3D) images were facilitated by the Allura 3D-RA software. [18] The study included 25 image pairs for radiographic evaluation obtained from both imaging techniques from 25 patients. For evaluation of the diagnostic quality of the images obtained from CBCT and MSCT scans, a senior radiologist, specialized in interpretation of images obtained from CBCT and MSCT, subjectively assessed each image pair twice (with an interval of one week between the first and second readings) using a five-point scale, [16] for factors such as accurate detection of findings (internal structure, margin of the lesions), subjective image quality (resolution, noise, contrast), and effects of artifacts on the region of interest (ROI).

The image from the MSCT was used as a reference image (gold standard) and the quality of the CBCT images was evaluated using the following five-point scale, as suggested by Hashimoto et al. [16]

Score 1:

The CBCT image was clearly inferior to the MSCT image.

Score 2:

The CBCT image was slightly inferior to the MSCT image.

Score 3:

The CBCT image quality was the same as the MSCT image.

Score 4:

The CBCT image was slightly superior to the MSCT image.

Score 5:

The CBCT image was clearly superior to the MSCT image.

For radiation monitoring, radiation absorbed dose, effective dose (E), and risk of fatal cancer were recorded and compared between CBCT and MSCT. For comparison of a radiation-absorbed dose, the 'dose area product' (DAP) values in milligray-centimeters squared (mGy-cm 2 ) of CBCT were converted to the 'dose length product' (DLP) in mGy-cm, using the conversion factor, as reported by Ogden K and Huda W (2009); [19] that is, a DLP of 1 mGy-cm corresponded to a DAP of 19 mGy-cm 2 .

This DLP was then multiplied with the 'conversion coefficient' (CC), that is, 0.0021 mSv/mGy-cm, for CT head procedures, as reported by the Diagnostic Imaging Council CT Committee Task Group #23 in the American Association of Physicists in Medicine (AAPM) report No. 96, [20] to derive the effective dose (E) in mSv. According to this report, an effective dose could be predicted by the following equation:

E (in mSv) ≈ 0.0021 (mSv/mGy-cm) × DLP (in mGy-cm)

For comparison of the effective dose (E, in mSv), the values obtained from the above formula were compared between CBCT and MSCT.

For assessing and comparing the radiation risk for fatal cancer for CBCT and MSCT techniques, the respective effective doses (E) were multiplied by the 'detriment-adjusted nominal risk coefficient', that is, 5 × 10−2 Sv -1 , as suggested by the International Commission on Radiological Protection (ICRP) 1990. [21] The fatal cancer risk was calculated according to the age groups, as described by ICRP 1990, in the multiplicative risk projection model [Table 1]. [21]
Table 1: Risk in relation to age based on the multiplicative risk projection model averaged for two sexes (male and female)[22]

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The dimensional accuracy was evaluated by comparing the linear measurements of the lesions, in millimeters, calculated on multiplanar reformations (MPR) in the axial, coronal, and sagittal sections, from images acquired by CBCT and MSCT. The outermost extents on both the ends were considered as the limit while calculating the linear distances. The maximum distance for a particular lesion on individual sections (axial/coronal/sagittal) were considered. In this study, MSCT was used as the gold standard for evaluating the linear measurement on images acquired by CBCT. After collecting all the necessary data, the findings were recorded in a proforma and were later transferred to a master chart. This data was then subjected to statistical analysis.


   Results Top


In this cross-sectional study, a total of 28 lesions were obtained from 25 patients. The age ranged from 18 to 74 years, with a mean age of 41.6 years, with a standard deviation of ± 17.08 years. Out of these 25 patients, 13 were male and 12 were female. The detailed distribution of the patients and the lesion's location are mentioned in [Table 1], [Table 2], [Table 3].
Table 2: Contingency analysis of jaw involvement (maxilla/mandible) according to the type of lesion for 28 lesions in 25 subjects

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Table 3: Distribution of the site of involvement (anterior/posterior/anteroposterior)

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When assessing the diagnostic quality of the paired images obtained from the 25 patients, the scoring suggested that the internal structures of the lesions, as seen on the CBCT-derived images, were slightly inferior (mean score = 2.03) to the images derived from the MSCT procedures. However, the margins of the lesions as seen on the CBCT images were similar in quality to those of the MSCT images (mean score = 3). Also, the subjective image quality of the CBCT-derived images was of the same quality as that of the MSCT-derived images (mean score = 3). The scoring suggested that the evidence of artifacts and their effects on the ROI were more obtrusive in CBCT-derived images as compared to MSCT derived images (mean score = 2.7). [Table 4] shows the kappa agreement conducted for intraobserver reliability during the assessment of the diagnostic quality of the radiographic images obtained from CBCT and MSCT procedures in the 25 patients.
Table 4: Kappa coefficient (k) for intraobserver reliability and strength of intraobserver agreement in the assessment of diagnostic quality of CBCT-acquired images in 25 subjects

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For the margins of the lesions and subjective image quality, 100% agreement was obtained that the diagnostic quality of CBCT-derived images was the same as that of MSCT-derived images. For internal structures of the lesion, a substantial agreement (k = 0.69) was obtained, while for the effects of the artifacts on the ROI, a moderate agreement (k = 0.58) was obtained. [Table 5] shows the intraobserver agreement for the visibility of the internal structure and artifacts on CBCT-derived images among the three groups of lesions. Interestingly, for malignant tumors of the jaws there was 91.6% agreement (perfect agreement, k = 0.802) that the visibility of internal structures on CBCT derived images were clearly inferior to the MSCT image (mean score = 1.91).
Table 5: Kappa coeffi cient (k) for intraobserver reliability and strength of intraobserver agreement in the assessment of the diagnostic quality of internal structures (IS) and artifacts (A) in three groups of lesions (cysts / benign lesions / malignant lesions) on CBCT-derived images in 25 subjects

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The radiation-absorbed doses for CBCT and MSCT in mGy-cm were 396.08 (±70.80) and 731.67 (±115.22), respectively [Table 6]. On statistical comparison, the absorbed doses for MSCT were significantly higher than those for the CBCT procedure. The mean E for CBCT and MSCT were 0.8314 (±0.149) mSv and 1.5361 (±0.242) mSv, respectively [Table 7]. The statistical analysis suggested that the effective dose (E) for MSCT was significantly higher than that for CBCT.
Table 6: Comparison of the radiation-absorbed doses for CBCT and MSCT in 25 subjects using student's paired t-test

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Table 7: Comparison of effective dose (E) for CBCT and MSCT procedures in 25 subjects using student's paired t-test

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[Table 8] shows the radiation risk for fatal cancer in different age groups for CBCT and the CT techniques, based on the multiplicative risk projection model (adapted from the European Commission 2004). The results clearly indicate that the risk of developing fatal cancer due to radiation was twice with MSCT (overall 84-in-a-million) as compared to CBCT (overall 49-in-a-million). Also the radiation risk was found to be reducing with an increasing age group. The statistics showed a significant difference in the mean radiation risk for CBCT and MSCT in all the age groups.
Table 8: Comparison of the radiation risk for stochastic effects (carcinogenesis) for CBCT and MSCT techniques according to the age groups using the multiplication factor (M.F.) from the multiplicative risk projection model[2,10]

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The mean linear measurements on MPR images in the axial, coronal, and sagittal sections were 25.53 mm, 15.67 mm, 23.57 mm, respectively, for CBCT and 26.58 mm, 17.33 mm, and 22.57 mm, respectively, for MSCT in the 28 lesions from 25 subjects [Table 9]. There were no statistically significant differences between the linear measurements of CBCT and MSCT for all the three sections (axial, coronal, and sagittal). Furthermore, a comparison was also done between the lesions (cysts/benign lesions/malignant lesions); but no statistically significant differences were found in the linear measurements of CBCT and MSCT in all the three sections, except for the axial section in the benign lesions, which showed a statistically significant difference in the linear measurements, with the CBCT measurements being lower than the MSCT measurements [Table 10].
Table 9: Descriptive statistics and comparison of the linear measurements (mm) on MPR images in the axial, coronal, and sagittal sections for CBCT and MSCT in 28 lesions from 25 subjects

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Table 10: Comparison of the linear measurements (mm) on MPR images in the axial, coronal, and sagittal sections for CBCT and MSCT among the lesions (cysts/benign lesions/malignant lesions) involving the jaws in 28 lesions from 25 subjects using one-way analysis of variance (ANOVA)

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   Discussion Top


The terms 'dose' and 'exposure' are widely used, but often misunderstood. 'Doses' may be measured for particular tissues or organs (e.g., skin, eye, bone marrow) or for the whole body, while 'exposure' usually refers to the equipment settings (time, mA, kV). [21] The collective effective dose quantity is an instrument for optimization, for comparing radiological technologies and protection procedures, predominantly in the context of occupational exposure. [22] The effective dose (E) is calculated by multiplying the actual organ doses by the risk-weighting factors related to the sensitivity of an individual organ. [23]

In the present study, the mean radiation doses given to 25 patients with the CBCT and MSCT technologies were 396.08 mGy-cm and 731.67 mGy-cm, respectively. It was statistically evident that the absorbed dose with CT was significantly (P < 0.05) higher than that of CBCT. The mean E for CBCT and MSCT were 0.8314 mSv and 1.5361 mSv, respectively. This indicated that the CBCT doses were almost half of those with MSCT. Our findings were in accordance with the previous studies, [16],[24],[25],[26] which suggested that CBCT showed a lower radiation dose than MSCT.

In the present study, the findings showed that there was a risk of fatal cancer of around 49-in-a-million with CBCT and a risk of 84-in-a-million with MSCT. The findings of the present study suggested that the risk of carcinogenesis was half with CBCT as compared to MSCT.

The linear measurements for the CBCT-derived images in the MPR sections were statistically similar to those with the MSCT scans. Overall, the linear measurements in CBCT-derived images were found to underestimate the dimensions, as compared to those with MSCT-derived images, but these were not statistically significant. Interestingly, in cases with a malignant lesion, CBCT-derived images were found to overestimate the dimensions in the axial and sagittal sections. However, these were also statistically not significant. Nevertheless, in the axial section of benign lesions the CBCT was found to significantly underestimate the linear measurement in comparison to the CT measurements. The findings of the present study were similar to those observed in the previously documented studies. [27],[28],[29],[30]

Diagnostic image quality assessments are often based on subjective measurements. [31] Studies [2],[16],[32],[33],[34],[35],[36] have reported evaluation of image quality, which has been based on subjective analysis, that is, visualization of the anatomical landmarks. Some other studies [16],[32],[33],[34],[35],[36] compared the image quality of CBCT with that of MSCT scanners, which served as the reference imaging method. In the present study, the reference imaging method was utilized in which the diagnostic quality of images derived from CBCT was compared with that of MSCT. On scoring, the internal soft tissue resolution of all the lesions on CBCT-derived images was slightly or clearly inferior (score 2 or 1) to that of the CT-derived images. On evaluating the image quality assessment in terms of the margin of the lesions, the overall scoring (score 3) implicated that the ability to distinguish the margin of the lesions was equal for both CBCT- and MSCT-derived images. This finding was in agreement with the previously reported studies. [3],[4],[15],[33],[34],[35],[36] From these findings, the key point noticed was the ability to distinguish cysts or benign tumors from the malignant tumors based on the assessment of the margins of the lesions on the CBCT-derived images. Previous studies have claimed CBCT to be superior to MSCT, in terms of imaging of high-contrast structures. [4],[16],[32],[34] However, in the present study, all the image pairs showed equal diagnostic quality in terms of imaging of the margins of the lesions. A 100% intraobserver agreement was observed in terms of the image quality of CBCT and MSCT for delineating the margins of the lesions being equal for both.

The subjective image quality in terms of contrast, noise, and resolution of CBCT-derived images was equal to that of MSCT-derived images. A 100% intraobserver agreement was observed for the same. Our findings were in agreement with other previous studies, [15],[16],[32],[36] which suggested that the subjective image quality (high resolution and contrast, better image noise level) could be considered as the same for both the imaging modalities - CBCT and MSCT.

In this study, all the paired images derived from the CBCT and CT techniques were evaluated by an observer for detection of artifacts and its effects on the ROI. There was a moderate intraobserver agreement (k = 0.58) that the artifact had a greater effect on the ROI in CBCT than in the MSCT images. The artifact was found to degrade the image quality of CBCT in at least five (20%) cases. The artifacts and their effects on the ROI were more commonly observed in the axial section. Interestingly, in a case of benign tumor, the effect of the artifact over the ROI was more in MSCT than in CBCT.

There are certain limitations in this study. The available technologies used were not the latest in the current situation for both the imaging modalities. The CBCT unit available for this study did not provide a grayscale value for the structures as seen in MSCT, which restricted the diagnostic efficacy of the soft tissue lesions. The lesions evaluated in this study did not include low-contrast lesions such as infectious and inflammatory lesions (periapical abscess, osteomyelitis, osteonecrosis, and orofacial soft tissue lesions), which limited the spectrum of the lesions to which the results could be applied. A further study is deemed necessary, with the latest technology and with a wider spectrum of lesions, using different exposure settings, to assess the diagnostic efficacy of CBCT over MSCT.


   Conclusion Top


As of now, CBCT may be more convenient and suitable than MSCT for the evaluation of bony lesions of the jaws caused by cysts and tumors. However, where evaluation of soft tissues is required as part of the patient's radiological assessment, the appropriate initial imaging should be CT or MRI, rather than CBCT.

 
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    Tables

  [Table 1], [Table 2], [Table 3], [Table 4], [Table 5], [Table 6], [Table 7], [Table 8], [Table 9], [Table 10]



 

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